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QPQUIN. �. THOMAS M.GAU P.O.BOX 1810•1810 E.HAZELTON AVENUE DIRECTOR STOCKTON,CALIFORNIA 96201 P• (209)468-3000 FAX(209)468-2999 �4c r F aa� www.sjgov.org/pubworks 0 FRITZ BUCHMAN DEPUTY DIRECTOR Wori&g for YOU MICHAEL SELLING DEPUTY DIRECTOR STEVEN WINKLER DEPUTY DIRECTOR ROGERJANES BUSINESS ADMINISTRATOR July 17, 2012 Mr. Todd Del Frate California Regional Water Quality Control Board Central Valley Region 11020 Sun Center Drive, #200 Rancho Cordova, California 95670-6114 SUBJECT: FIRST SEMESTER 2012 GROUNDWATER AND SURFACE WATER MONITORING REPORT; FOOTHILL SANITARY LANDFILL Dear Mr. Del Frate: Enclosed is the First Semester 2012 Groundwater and Surface Water Monitoring Report for the Foothill Sanitary Landfill. Groundwater monitoring continues on a semi-annual basis in accordance with our WDRs. Two VOCs, neither in excess of 1 ppb were reported in well MW-3. This well was free of VOCs from early 2002 until approximately five years after the placement of landfill liner material over Module "I" refuse. The reoccurrence of these compounds after years of non-detection is troublesome, especially when many of those years of non-detection were without a LFG collection system; however, this is consistent with a five-year lag time between "cause" on the surface and "effect" seen in the groundwater. The County continues to be concerned that placing an impermeable liner over refuse promotes movement of LFG towards the groundwater in spite of the presence of a LFG collection system. The enclosed report includes a review of the events at this site. In response to these detections, the County increased corrective action (landfill gas collection). Increase in LFG collection was accomplished by the replacement LFG well GX-2A and increase in LFG pipe size to better serve GX-7 and -9 in December 2011. These improvements were viewed during your inspection in December 2011. Collection of LFG from wells that may affect the pressures beneath the liner was increased weekly. The water level in MW-1 was sufficient to measure elevation, but not to collect a sample. This well is cross-gradient from the landfill, so data from this well is not needed at this time in evaluating the data from the up-gradient or down-gradient wells. However, this well is useful in estimating groundwater elevations under the site. Results of the data from the recent"rain year" at the Evapotranspiration (ET) closure cover test pad will be discussed in the next semiannual report. Previous data show that our ET cover performs twice as well as an intact prescriptive cover. Surface water and storm water was not available for sampling due to lack of rain.